The present invention relates generally to electronic devices, and more particularly, to a system and method for enhanced end station to end station data flow control in an available bit rate asynchronous transfer mode network.
The development of the asynchronous transfer mode (ATM) method of transferring data and information across a network has created a need to provide traffic management services within these ATM networks. In networks that connect end station systems having very disparate performance speeds, a transmitting end station can often send data at a rate faster than a receiving end station can process the data. A low buffer condition can occur in the receiving end station that must be remedied. Traffic management services provide mechanisms to deal with flow rate problems such as this.
One such traffic management service is the ATM Forum Traffic Management Specification Version 4.0 (the TM 4.0 specification). The TM 4.0 specification is an ATM Forum Standard that uses existing explicit forward congestion indication (EFCI) switches. The TM 4.0 specification describes an Available Bit Rate (ABR) Protocol for controlling data flow that can adapt the data flow rate according to changing network conditions, including congestion at network end stations. The ATM Forum TM 4.0 specification was written specifically to address the problem of managing flow traffic within the network, rather than the problem of data congestion control at network end stations. However, the network is not always the point of congestion. A receiving end station may not be able to process the transmitted data at the rate the data is being sent, while the network is fully capable of transporting data at the transmitted rate.
While the TM 4.0 specification allows the receiving end station to send a message in a Resource Management Cell (RM cell) to indicate to the transmitting end station to stop sending data (sometimes called an xe2x80x9cXOFFxe2x80x9d message) as well as a message in an RM cell to restart data flow (sometimes called on xe2x80x9cXONxe2x80x9d message), the TM 4.0 specification has a relatively slow restart after an XOFF message has been processed. The TM 4.0 specification requires the receiving end station to either 1) wait for a forward RM cell from the transmitting end station or 2) wait one hundred milliseconds in order to send an XON signal after sending an XOFF signal. Thus, in the case where the receiving end station, and not the network, limits the data flow, the TM 4.0 specification does not provide an adequate mechanism to quickly remedy temporary end station receiver congestion such as a low buffer condition.
Several conventional network traffic management services provide data flow control with varying degrees of XOFF/XON effectiveness. QFC provides an ATM traffic management service with the ability to send messages indicating XON and XOFF conditions. However, QFC is not an ATM Forum Standard and does not work with existing deployed EFCI switches. QFC provides an ATM network traffic management service with some XON/XOFF capability. However, QFC only provides XON/XOFF capability from the network to the end station. Thus, a receiving end station cannot send a message indicating an XON or an XOFF to a remote transmitting end station. TCP is a traffic management system that can provide end station to end station flow control. However, TCP is not ATM network specific and is very slow reacting to congestion/dropped data at a receiving end station. DIGITAL EQUIPMENT CORPORATION""s xe2x80x9cFLOWMASTERxe2x80x9d provides a proprietary traffic management service involving a mechanism where the receiver sends xe2x80x9ccreditsxe2x80x9d to the transmitter. When the transmitter uses up the credits, it must either get additional credits or stop transmitting. These conventional schemes do not, however, provide effective XOFF/XON functionality for ABR ATM networks.
The present invention provides an enhanced ABR ATM network end station to end station data flow control system and method that substantially eliminates or reduces disadvantages and problems associated with previously developed ABR ATM network data flow control systems and methods.
More specifically, the present invention provides a system and method for data flow control in an ABR ATM network. In the ABR ATM network, a transmitting end station transmits data to a receiving end station across the network. The transmitting end station sends forward resource management (RM) cells across the network, while the receiving end station sends backward RM cells across the network. The receiving end station contains a control module that can operate to stop or reduce data flow from the transmitting end station by sending an RM cell having a desired low data flow rate. The control module further operates to restart data flow to the receiving end station by sending a backward RM cell having a desired high data flow rate. In this way, the receiving end station has data flow control across the ATM network.
In a particular embodiment, a system for controlling data flow in an available bit rate asynchronous transfer mode network includes a transmitting end station that transmits data. A receiving end station receives the data transmitted by the transmitting end station and transmits a first unsolicited RM cell having a desired low data flow rate upon detecting congestion at the receiving end station. The receiving end station also transmits a second unsolicited RM cell having a desired high data flow rate upon detecting an absence of congestion at the receiving end station.
In a specific embodiment, the present invention provides a mechanism to allow a receiving end station to send XON and XOFF messages within a backward RM cell to a transmitting end station in an ATM network that is ATM Forum TM 4.0 ABR managed without waiting for a forward RM cell or for one hundred milliseconds to pass.
The present invention provides a technical advantage by enhancing end station to end station data flow traffic management in an ABR ATM network. The present invention allows a receiving end station to restart data flow at a rate set by the receiving end station. The present invention also allows the receiving end station to stop (or reduce) and restart data flow without waiting for the transmitting end station""s forward RM cell. In a particular embodiment, the receiving end station generates unsolicited RM cells immediately upon detecting the congestion status at the receiving end station. As such, the present invention allows a receiving end station to stop or reduce data flow prior to a catastrophic overload that can cause data loss. This XON/XOFF capability is a technical advantage of the present invention.
The present invention provides another technical advantage by providing a standards-based data flow control system that works with existing EFCI switches.
Specifically, the present invention provides a technical advantage by interworking with other implementations of network switches and end stations that are fully compliant with the ATM Forum TM 4.0 specification. The present invention can use RM cells as defined in the TM 4.0 specification to provide the receiving end station with XON and XOFF capability without the slow start problems required under the existing TM 4.0 specification for an ABR protocol.